World War 2 is now pretty remote for most people, but for the residents of Southend and Sheerness it can seem uncomfortably close, in the form of a sunken ship carrying 1,400 tonnes of potentially unstable high explosives.

The SS Richard Montgomery is a merchant vessel built to the standard World War 2 'Liberty Ship' design in 1943. After D-Day she came under orders to supply the forces in France. On route she was ordered by naval authorities based on Southend pier to anchor at the Great Nore Anchorage, between Sheerness and Southend.

On 20 August 1944 she dragged her anchor and ran aground in 24 feet of water, five miles off Southend and less than two miles from Sheerness. The falling tide led her to break her back, and a company was ordered to salvage her cargo of munitions. They recovered the cargo in the aft section, but the holds forward flooded and the cargo could not be recovered.

1,400 tonnes of munitions remain to this day, including 286 2,000 lb bombs, 4,439 1,000 lb bombs, 1,925 500 lb bombs, 2,815 fragmentation bombs and various phosphorus bombs, charges etc. The ship's masts are still clearly visible above water, and the ship is surrounded by an exclusion zone which is monitored continuously by the Maritime and Coastguard Agency.

Debate still continues about just how dangerous the wreck is, and why it has never been properly dealt with. Certainly such an operation would be extremely delicate and expensive, though there has also been an argument for leaving well alone – a Polish cargo ship, the 'Kielce', exploded in 1946 during salvage work and damaged roofs, chimneys and windows in nearby Folkestone. Its explosives load was much smaller.

The more extreme claims suggest that an explosion of the Richard Montgomery's cargo would cause a tsunami with a wave sixteen feet high (a 1970 BBC News report) or four feet high (a 2012 report). There would be structural damage in Sheerness, and windows broken in Southend, with possible flooding from the wave.

Others minimise these fears, and also say that the danger of explosion is 'remote'. Nevertheless, the presence of this hazard put a dampener on the proposals for a London airport in the Thames, and critics argue that while fuses may be sodden, new dangers have arisen from chemical reactions producing the very sensitive explosive copper azide. World War 1 explosives in sodden ground in Belgium and France still cause fatalities each year.

A New Scientist investigation in 2004 concluded that a collision, deliberate attack or shifting of the cargo could produce a large explosion. Regular underwater surveys show that the vessel continues to deteriorate, and a contract is being issued for the removal of the masts because of the strain they place on the deck.

In spite of this, Southend residents are philosophical about the dangers, and the ship (sometimes known as the 'Doomsday Ship') is the subject of wry jokes.